In the development of a multi-channel prosthesis, data from the study of radially versus longitudinally arranged pairs of electrodes relative to the spiral lamina, the effects of distance between electrode pairs, and the electroanatomy of the cochlear tissues and fluids, suggest that electrode pairs should be close together and in close proximity to neural elements of the spiral lamina to maximize channel independence in multi-electrode devices. Data concerning insertion trauma and safe limit of stimulation, suggests that the implant size should be small and that electrode surface areas should be large and sufficiently removed from excitable elements to minimize the effects of very high local current densities at their surfaces on these tissues. In addition, existing evidence supports the view that we may lose little in perceptual benefits and gain significantly in safety characteristics by placing electrodes outside the otic capsule.
The technical difficulties with the development of such a multi-channel middle ear system include the creation of precise holes through the bony lateral wall with minimum damage to the underlying cochlear tissues at predetermined sites, and the anchoring of stimulating electrodes in the fenstrae.
In the past, several types of devices have been used to anchor electrodes. Examples of such anchoring devices are disclosed in U.S. Pat. No. 4,462,402, issued Jul. 31, 1984, to Burgio et al.; U.S. Pat. No. 4,487,210, issued Dec. 11, 1984, to Knudsen et al.; U.S. Pat. No. 4,612,915, issued Sept. 23, 1986, to Hough et al.; and U.S. Pat. No. 4,606,329, issued Aug. 19, 1986, to Hough. The problem is that these anchoring devices have been used at bony sites of the body, including recently, the temporal bone, but not the otic capsule.